In the injured lung, damage to the alveolar epithelium initiates repair mechanisms that if successful are associated with a recovery of lung function and survival but if unsuccessful result in pulmonary fibrosis and death or disability. The three projects that comprise this proposal examine mechanisms by which the alveola epithelium responds to stimuli present in the milieu of the injured lung and the consequences of these responses for alveolar epithelial repair or fibrosis. To take advantage of the power of mouse genetics, all of the investigators propose studies in mouse models of acute lung injury or fibrosis. The physiology and mouse core will provide the project investigators with standard models of lung injury and fibrosis and perform detailed physiologic measurements of alveolar epithelial function in these models. The core will also breed and genotype transgenic and knockout mouse populations for the project investigators and oversee the expression of Cre recombinase in the lung epithelium. This program project is committed to examining the role of the alveolar epithelium in the development of lung injury. To achieve this goal in the in vivo mouse model, we will create transgenic mouse systems that will allow for the inducible expression or knockout of specific proteins in the entire lung epithelium, or exclusively in Type II or Type I alveolar epithelial cells